Upsert the attribute value for an end user entity attribute source

curl --request POST \
  --url https://app.herondata.io/api/end_users/{end_user_heron_id}/entities/{entity_name} \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '{
  "attribute_name": "<string>",
  "source_heron_id": "<string>",
  "value": "<any>"
}'

{
  "end_user_entity_attribute": {
    "attribute_description": "<string>",
    "attribute_name": "<string>",
    "attribute_sources": [
      {
        "heron_id": "<string>",
        "sort_order": 123,
        "source_config": {},
        "source_type": "parsed_end_user_file"
      }
    ],
    "attribute_type": "float",
    "heron_id": "<string>",
    "reconciliation_config": {},
    "reconciliation_strategy": "sort_order"
  },
  "end_user_entity_attribute_source": {
    "heron_id": "<string>",
    "sort_order": 123,
    "source_config": {},
    "source_type": "parsed_end_user_file"
  },
  "heron_id": "<string>",
  "value": "<any>"
}